1. Field of the Invention
This invention relates to oxyfluoride phosphors, and white light emitting diodes (LEDs) including the oxyfluoride phosphor for solid state light applications.
2. Description of the Related Art
(Note: This application references a number of different publications as indicated throughout the specification by one or more reference numbers within brackets, e.g., [x]. A list of these different publications ordered according to these reference numbers can be found below in the section entitled “References.” Each of these publications is incorporated by reference herein.)
In order to generate white light from LEDs, there are basically two strategies: the first approach is to mix different red, green, and blue components from LED chips, and the second approach is to down-convert the emission from a blue LED or ultraviolet (UV) LED to a longer wavelength using a phosphor.
For generating white light, most current commercial LED lamps employ the second approach, namely using yellow emitting YAG:Ce3+ phosphors excited by blue InGaN diodes, because of its superiority in terms of cost, efficiency and simplicity of fabrication [1-3]. Further information on the second approach can be found in PCT International Patent Application No. WO98/05078 [4], which is incorporated by reference herein.
However, YAG:Ce3+ phosphors have relatively weak light emitting intensity in the red spectral region and, consequently, it is difficult to obtain a good color rendering index (CRI) [5-7]. In addition, the output color from YAG:Ce3+ phosphors is strongly dependent on temperature and current, which will become a significant problem in high-power LEDs [8].
To overcome these drawbacks, and also to avoid issues associated with intellectual property, there are extensive efforts worldwide to develop new yellow emitting phosphors for blue-pumped LED applications [9-12], as well as to optimize existing systems. Unfortunately, with the exception of YAG:Ce3+, there are few phosphor materials for use with long UV or blue excitation sources. Up to now, no competing yellow phosphor has been found to replace the YAG:Ce3+ phosphor.
Thus, there is a need in the art for the development of new phosphors for solid-state lighting, especially phosphors with high efficiency and improved color rendering properties in the red region, that can be manufactured easily and at low cost, with better thermal stability. The present invention satisfies that need.